The power supply for a backlight source of a TFT LCD panel makes use of an inverter circuit to accomplish energy conversion and drive a cold cathode fluorescent lamp (CCFL) to be on. Conventional inverter circuits can be divided into half-bridge type, full-bridge type and push-pull type according to different circuit topologies. An inverter circuit is a circuit for converting a DC power into an AC power.
As shown in FIG. 1, a transformer T1 divides the circuit into a front-end circuit at the primary side 101 and a rear-end circuit at the secondary side 102. The front-end circuit at the primary side 101 comprises a DC voltage source Vcc, a first switch Q1, and a second switch Q2. The rear-end circuit at the secondary side 102 comprises at least a capacitor (C1, C2, C3), a load, and at least a diode (D1, D2). A push-pull type control chip 103 is connected between the front-end circuit at the primary side 101 and the rear-end circuit at the secondary side 102. Please also refer to FIG. 2. The push-pull type control chip 103 outputs a first control signal a and a second control signal b for controlling switching actions of the two switches Q1 and Q2 at the primary side 101, respectively. The DC power source Vcc is used to provide energy, and the transformer T1 raises and converts the voltage of the DC power Vcc to the rear-end circuit 102 for driving the load. The output voltage waveform c at the secondary side of the transformer T1 is the voltage waveform at point C. As shown in FIG. 2, the output voltage waveform c at the secondary side is an AC voltage waveform.
In the above description, the push-pull type control chip 103 is produced by Linfinity (Microsemi) Corporation with type of LX1686.
As shown in FIG. 3, a transformer T2 divides the circuit into a front-end circuit at the primary side 201 and a rear-end circuit at the secondary side 202. The front-end circuit at the primary side 201 comprises four electronic switches (P1, P2, N1, and N2), a full-bridge type control chip 203, and a capacitor C1. The rear-end circuit at the secondary side 202 comprises a load. Please also refer to FIG. 4. The full-bridge type control chip 203 outputs four control signals POUT1, POUT2, NOUT1, and NOUT2 for controlling switching actions of the four electronic switches P1, P2, N1, and N2, respectively. The DC power source Vcc is used to provide energy, and the transformer T2 raises and converts the voltage of the DC power Vcc to the rear-end circuit 202 for driving the load. The full-bridge type control chip 203 is produced by Beyond Innovation Technology with the type of BIT3105.
As shown in FIG. 5, a transformer T3 divides the circuit into a front-end circuit at the primary side 301 and a rear-end circuit at the secondary side 302.
The front-end circuit at the primary side 301 comprises a DC voltage source Vcc, two electronic switches (Q1, Q2), a half-bridge type control chip TL494, two capacitors (C1, C2) and an isolation transformer Tr. The rear-end circuit at the secondary side 302 comprises a load. Please also refer to FIG. 6. The half-bridge control chip TL494 outputs control signals D1–D2 via two output terminals D1 and D2. The control signals D1–D2 control switching actions of the two electronic switches Q1 and Q2 via the isolation transformer Tr, respectively. The two electronic switches Q1 and Q2 are n-channel FETs or p-channel FETs. Through switching actions of the two electronic switches Q1 and Q2, electric energy stored in the capacitors C1 and C2 can be transferred to a primary side terminal T31 of the transformer T3 via a coupling capacitor C3 to form an AC power source ac. The voltage of the capacitors C1 and C2 is a half (Vcc/2) of the DC voltage Vcc. The AC power source ac is used to provide energy for the transformer T3, which boosts and converts the ac power source to the secondary side 302 for driving the load.
Please refer to FIG. 7. An inverter circuit 40 and a control chip 42 are connected and disposed on the same printed circuit board. If the used inverter circuit 40 is of the full-bridge type, a full-bridge type control chip 42 needs to be matched for normal operations, if the used inverter circuit is of the half-bridge type, a half-bridge type control chip needs to be matched for normal operations, and if the used inverter circuit is of the push-pull type, a push-pull type control chip needs to be matched for normal operations. Therefore, there is less flexibility and commonality in practical use. Moreover, use of the inverter circuit 40 is usually limited by the control chip 40 to cause malfunction of the inverter circuit 40.
1. Field of the Invention
The present invention relates to a modularized inverter control circuit and, more particularly, to a control circuit making use of a push-pull type control IC to connect other accessory circuit units and packaged and disposed on a printed circuit board to accomplish modularization for driving and control of various inverter circuits.
2. Description of Related Art